Conventional plastic optical fibers, which are generally stretched in the course of the production, tend to shrink at a temperature higher than about 80.degree. C. For example, when they are heated to a temperature of 120.degree. C. for a very short period of time, for example several seconds, they shrink to about 50% of their original length.
The conventional plastic optical fiber is usually made of an amorphous polymer such as poly(methyl methacrylate) (hereinafter referred to as "PMMA") and polystyrene, and only stretching of the optical fiber can impart good mechanical properties such as flexibility and pliability to the optical fiber. Therefore, it has been believed to be impossible to avoid the shrinkage of the plastic optical fiber at a high temperature.
The present invention has been developed to overcome the above described drawbacks of the conventional plastic optical fibers and to provide a plastic optical fiber having good heat resistance and flexibility as well as good light transmission.